Disk drive decreasing a settle delay based on speed that a settle parameter adapts

ABSTRACT

A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of tracks, and control circuitry operable to seek the head to a target track and settle the head on the target track during a settle time, adapt a settle parameter used to settle the head on the target track, access the target track after an access delay, and decrease the access delay based on a speed that the settle parameter adapts.

BACKGROUND

Disk drives comprise a disk and a head connected to a distal end of anactuator arm which is rotated about a pivot by a voice coil motor (VCM)to position the head radially over the disk. The disk comprises aplurality of radially spaced, concentric tracks for recording user datasectors and servo sectors. The servo sectors comprise head positioninginformation (e.g., a track address) which is read by the head andprocessed by a servo control system to control the velocity of theactuator arm as it seeks from track to track.

Because the disk is rotated at a constant angular velocity, the datarate is typically increased toward the outer diameter tracks (where thesurface of the disk is spinning faster) in order to achieve a moreconstant linear bit density across the radius of the disk. To simplifydesign considerations, the data tracks are typically banded togetherinto a number of physical zones, wherein the data rate is constantacross a zone, and increased from the inner diameter zones to the outerdiameter zones. This is illustrated in FIG. 1, which shows a prior artdisk format 2 comprising a number of servo tracks 4 that define the datatracks, wherein the data tracks are banded together to form a pluralityof zones.

The prior art disk format of FIG. 1 also shows a number of servo sectors6 ₀-6 _(N) that define the servo tracks 4, wherein the data tracks areaccessed relative to the servo tracks 4. Each servo sector 6 _(i)comprises a preamble 8 for storing a periodic pattern, which allowsproper gain adjustment and timing synchronization of the read signal,and a sync mark 10 for storing a special pattern used to symbolsynchronize to a servo data field 12. The servo data field 12 storescoarse head positioning information, such as a track address, used toposition the head over a target data track during a seek operation. Eachservo sector 6 _(i) further comprises groups of servo bursts 14 (e.g.,A, B, C and D bursts), which comprise a number of consecutivetransitions recorded at precise intervals and offsets with respect to adata track centerline. The groups of servo bursts 14 provide fine headposition information used for centerline tracking while accessing a datatrack during write/read operations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servosectors that define a plurality of servo tracks.

FIG. 2A shows a disk drive according to an embodiment of the presentinvention comprising a head actuated over a disk.

FIG. 2B is a flow diagram according to an embodiment of the presentinvention wherein after seeking to a target track a settle parameter isadapted and an access delay is decreased based on a speed of the settleparameter adapting.

FIG. 2C illustrates the access delay decreasing as the adapting speed ofthe settle parameter decreases according to an embodiment of the presentinvention.

FIGS. 3A and 3B illustrate an embodiment of the present inventionwherein the settle parameter comprises a magnitude of a sinusoid thatestimates a repeatable runout (RRO) of the disk.

FIG. 4 is a flow diagram according to an embodiment of the presentinvention wherein an adapting delay is decreased based on the adaptingspeed of the settle parameter.

FIG. 5 is a flow diagram according to an embodiment of the presentinvention wherein the adapted settle parameter is saved after theadapting delay, and then used to initialize the settle parameter for thenext seek to the same track.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2A shows a disk drive according to an embodiment of the presentinvention comprising a head 16 actuated over a disk 18 comprising aplurality of tracks 20. The disk drive further comprises controlcircuitry 21 operable to seek the head to a target track and settle thehead on the target track during a settle time (step 22), adapt a settleparameter used to settle the head on the target track (step 24), accessthe target track (step 28) after an access delay (step 26), decrease theaccess delay based on a speed that the settle parameter adapts (step30), and repeat the flow diagram at least once starting at step 22.

In the embodiment of FIG. 2A, the disk 18 comprises embedded servosectors 32 ₀-32 _(N) that define a plurality of servo tracks 20. Thecontrol circuitry 21 processes a read signal 34 emanating from the head16 to demodulate the servo sectors 32 ₀-32 _(N) and generate a positionerror signal (PES) representing an error between the actual position ofthe head and a target position relative to a target track. The controlcircuitry 21 filters the PES using a suitable compensation filter togenerate a control signal 36 applied to a voice coil motor (VCM) 38which rotates an actuator arm 40 about a pivot in order to actuate thehead 16 radially over the disk in a direction that reduces the PES. Theservo sectors 32 ₀-32 _(N) may comprise any suitable positioninformation, such as a track address for coarse positioning and servobursts for fine positioning. The servo bursts may comprise any suitableservo burst pattern, such as an amplitude based servo burst pattern(e.g., A,B,C,D quadrature pattern) shown in FIG. 1, or a phase basedservo burst pattern (e.g., N,Q servo bursts).

In one embodiment, when the control circuitry 21 seeks the head 16 to atarget track, one or more settle parameters are used to settle the headonto the target track during a settle interval. In an example describedbelow, the settle parameters may comprise a magnitude of a sinusoid thatestimates a repeatable runout (RRO) of the disk 18. The sinusoid may beused to generate feedforward compensation values so that the headfollows the RRO while settling onto the target track (and while trackingthe centerline of the target track). In one embodiment, it may takeseveral seeks (e.g., a hundred seeks) for the settle parameters toconverge. That is, during the settle interval of each initial seek thesettle parameters are adapted, and after a number of seeks, the settleparameters converge toward optimal values. At the beginning of thelearning seeks, the settle parameters are typically suboptimal, andtherefore an access delay associated with accessing the track (write orread) is increased to allow more time for the head to settle onto thetrack, thereby avoiding off-track writes and or slipped revolutions.This is illustrated in FIG. 2C wherein the access delay is initializedto a high value at the beginning of the learning seeks. Then as theadapting speed of the settle parameters decreases (meaning that thesettle parameters are converging), the access delay is decreased so thatthe track can be accessed sooner.

FIGS. 3A and 3B illustrate an embodiment of the present inventionwherein the settle parameter comprises a magnitude A of a sinusoid(Ae^(jθ)) that estimates a repeatable runout (RRO) of the disk, where θrepresents the phase of the sinusoid having an angular frequency of2πk/N (k is a current servo sector out of N servo sectors). During afirst seek to a target track, the magnitude A adapts to a first value 42₀ during an adapting delay which may be the same or different than theaccess delay. During the next seek to the target track, the magnitude Afurther adapts to a second value 42 ₁ during the adapting delay. In oneembodiment, the difference in the magnitude ΔA of the sinusoid at theend of the adapting delay represents the speed at which the settleparameter is adapting. That is, the control circuitry 21 measures thespeed that the settle parameter adapts by measuring a difference betweenthe settle parameter over an interval, wherein in one embodiment theinterval corresponds to the adapting delay of consecutive seeks. In analternative embodiment, the interval for measuring the difference in thesettle parameter may span at least part of a single settle time for asingle seek (e.g., beginning to end of the adapting delay). Asillustrated in FIGS. 3A and 3B, the adapting speed of the settleparameter decreases as the number of seeks increases, with acorresponding decrease in the delay (access delay and/or adaptingdelay).

In one embodiment, the control circuitry 21 measures the speed that thesettle parameter adapts according to:

speed[k]=(1−α)speed[k−1]+α(p[k]−1])

where k−1 and k represent a beginning and end of the interval, α is ascalar, and p is the settle parameter. The above equation operates tofilter out outliers in the adapting speed measurements so that theaccess delay decreases without significant transients. However, theabove equation is optional, or may be modified into any suitablefiltering function.

FIG. 4 is a flow diagram according to an embodiment of the presentinvention wherein the control circuitry is operable to seek the head toa target track and settle the head on the target track during a settletime (step 44), and adapt a settle parameter over an adapting delay ofthe settle time (step 46), wherein the settle parameter is used tosettle the head on the target track. After the adapting delay (step 48),the adapting delay is decreased based on a speed that the settleparameter adapts (step 50), and the flow diagram is repeated at leastonce starting at step 44.

Referring again to the example of FIG. 3A, the adapting delay isinitialized to a long value to allow the settle parameter to adaptlonger at the beginning of the learning seeks. As the adapting speeddecreases, the adapting delay decreases. In one embodiment, the adaptingdelay is decreased to account for changes in an adaptation profile ofthe settle parameter. In the example of FIG. 3A, the magnitude A of theRRO sinusoid rises to a peak during the settle interval, and thendecreases as the head is tracking the target track. The time to the peakin the adaptation profile may decrease as the adapting speed of thesettle parameter decreases as illustrated in FIG. 3A. Therefore, in oneembodiment the adapting delay is initialized based on an expected peakin an adaptation profile of the settle parameter, and then decreased soas to substantially track the location of the peak in the adaptationprofile. In one embodiment, the initial adapting delay and/or theinitial access delay may span multiple revolutions of the disk whereasthe final adapting delay and/or access delay may span a fraction of arevolution (e.g., a tenth of a revolution).

In one embodiment, the initial adapting delay may equal the initialaccess delay, but the final adapting delay may be greater than the finalaccess delay. For example, in FIG. 3A the final adapting delay may belimited to delay 52 whereas the access delay may be decreased to delay54. The shorter access delay allows the target track to be accessedsooner while allowing the settle parameter to continue adapting for awhile longer (e.g., until the peak is reached in the adaptation profileas described above).

FIG. 5 is a flow diagram according to an embodiment of the presentinvention wherein after seeking the head to a target track (step 56),the settle parameter is initialized at the beginning of the settleinterval with a value saved from a previous seek (step 58). The settleparameter is then adapted for the current seek (step 60). When theadapting delay is reached during the settle interval (step 62), theadapted value of the settle parameter is saved (step 64), and at leastone of the adapting delay and the access delay is decreased based on theadapting speed of the settle parameter (step 66). The target track isthen accessed by performing a write or read operation (step 68). Whenanother seek is performed to the same track (step 56), at the beginningof the settle interval the settle parameter is initialized (step 58)with the value saved at step 64.

In one embodiment, the settle parameter may continue adapting during theaccess operation, but is initialized with the value saved at the end ofthe adapting delay. As described above, initializing the settleparameter based on the end of the adapting delay of the previous seekoperation may help track a peak in an adaptation profile of the settleparameter as illustrated in the example of FIG. 3A.

In one embodiment, the tracks of the disk may be banded together todefine a plurality of zones, wherein a different value may be used forthe settle parameters for each zone. That is, there may be multiple setsof settle parameters where each set corresponds to a zone, and each setmay be adapted when the control circuitry seeks the head into therespective zone. In one embodiment, the control circuitry may adapt thesettle parameters of a zone only when the seek length to reach the zoneexceeds a threshold. That is, the settle parameters may exhibit aparticular characteristic (such as the overshoot peak in FIG. 3A) whenthe seek to the zone exceeds a threshold. In one embodiment when thecontrol circuitry executes a shorter seek, the settle parameters are notchanged (i.e., the current value of the settle parameters are used aftera short seek).

Any suitable control circuitry may be employed to implement the flowdiagrams in the embodiments of the present invention, such as anysuitable integrated circuit or circuits. For example, the controlcircuitry may be implemented within a read channel integrated circuit,or in a component separate from the read channel, such as a diskcontroller, or certain steps described above may be performed by a readchannel and others by a disk controller. In one embodiment, the readchannel and disk controller are implemented as separate integratedcircuits, and in an alternative embodiment they are fabricated into asingle integrated circuit or system on a chip (SOC). In addition, thecontrol circuitry may include a suitable preamp circuit implemented as aseparate integrated circuit, integrated into the read channel or diskcontroller circuit, or integrated into an SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the steps of the flow diagrams describedherein. The instructions may be stored in any computer-readable medium.In one embodiment, they may be stored on a non-volatile semiconductormemory external to the microprocessor, or integrated with themicroprocessor in a SOC. In another embodiment, the instructions arestored on the disk and read into a volatile semiconductor memory whenthe disk drive is powered on. In yet another embodiment, the controlcircuitry comprises suitable logic circuitry, such as state machinecircuitry.

1. A disk drive comprising: a disk comprising a plurality of tracks; ahead actuated over the disk; and control circuitry operable to: (a) seekthe head to a target track and settle the head on the target trackduring a settle time; (b) adapt a settle parameter used to settle thehead on the target track; (c) access the target track after an accessdelay; (d) decrease the access delay based on a speed that the settleparameter adapts; and (e) repeat (a) through (d) at least once.
 2. Thedisk drive as recited in claim 1, wherein the control circuitry isfurther operable to measure the speed that the settle parameter adaptsby measuring a difference between the settle parameter over an interval.3. The disk drive as recited in claim 2, wherein the control circuitryis further operable to measure the speed that the settle parameteradapts according to:speed[k]=(1−α)speed[k−1]+α(p[k]−1]) wherein: k−1 and k present abeginning and end of the interval; α is a scalar; and p is the settleparameter.
 4. The disk drive as recited in claim 2, wherein the intervalspans at least part of a single settle time for a single seek.
 5. Thedisk drive as recited in claim 4, wherein the interval spans at leastpart of multiple settle times for multiple seeks.
 6. The disk drive asrecited in claim 1, wherein the settle parameter comprises a magnitudeof a sinusoid that estimates a repeatable runout (RRO) of the disk. 7.the disk drive as recited in claim 1, wherein the control circuitry isfurther operable to: adapt the settle parameter over an adapting delayof the settle time; save the settle parameter after the adapting delayof a first settle time of a first seek; further adapt the saved settleparameter over the adapting delay of a second settle time of a secondseek; and decrease the adapting delay based on the speed that the settleparameter adapts.
 8. The disk drive as recited in claim 7, wherein theadapting delay substantially equals the access delay.
 9. A disk drivecomprising: a disk comprising a plurality of tracks; a head actuatedover the disk; and control circuitry operable to: (a) seek the head to atarget track and settle the head on the target track during a settletime; (b) adapt a settle parameter over an adapting delay of the settletime, wherein the settle parameter is used to settle the head on thetarget track; (c) decrease the adapting delay based on a speed that thesettle parameter adapts; and (d) repeat (a) through (c) at least once.10. the disk drive as recited in claim 9, wherein the control circuitryis further operable to: access the target track after an access delay ofthe settle time; and decrease the access delay based on the speed thatthe settle parameter adapts.
 11. the disk drive as recited in claim 9,wherein the control circuitry is further operable to initialize theadapting delay based on a peak in an adaptation profile of the settleparameter.
 12. A method of operating a disk drive comprising, the diskdrive comprising a head actuated over a disk comprising a plurality oftracks, the method comprising: (a) seeking the head to a target trackand settle the head on the target track during a settle time; (b)adapting a settle parameter used to settle the head on the target track;(c) accessing the target track after an access delay; (d) decreasing theaccess delay based on a speed that the settle parameter adapts; and (e)repeating (a) through (d) at least once.
 13. The method as recited inclaim 12, further comprising measuring the speed that the settleparameter adapts by measuring a difference between the settle parameterover an interval.
 14. The method as recited in claim 13, furthercomprising measuring the speed that the settle parameter adaptsaccording to:speed[k]=(1−α)speed[k−1]+α(p[k]−p[k−1]) wherein: k−1 and k present abeginning and end of the interval; α is a scalar; and p is the settleparameter.
 15. The method as recited in claim 13, wherein the intervalspans at least part of a single settle time for a single seek.
 16. Themethod as recited in claim 15, wherein the interval spans at least partof multiple settle times for multiple seeks.
 17. The method as recitedin claim 12, wherein the settle parameter comprises a magnitude of asinusoid that estimates a repeatable runout (RRO) of the disk.
 18. themethod as recited in claim 12, further comprising: adapting the settleparameter over an adapting delay of the settle time; saving the settleparameter after the adapting delay of a first settle time of a firstseek; further adapting the saved settle parameter over the adaptingdelay of a second settle time of a second seek; and decreasing theadapting delay based on the speed that the settle parameter adapts. 19.The method as recited in claim 18, wherein the adapting delaysubstantially equals the access delay.
 20. A method of operating a diskdrive comprising a head actuated over a disk comprising a plurality oftracks, the method comprising: (a) seeking the head to a target trackand settle the head on the target track during a settle time; (b)adapting a settle parameter over an adapting delay of the settle time,wherein the settle parameter is used to settle the head on the targettrack; (c) decreasing the adapting delay based on a speed that thesettle parameter adapts; and (d) repeating (a) through (c) at leastonce.
 21. the method as recited in claim 20, further comprising:accessing the target track after an access delay of the settle time; anddecreasing the access delay based on the speed that the settle parameteradapts.
 22. the method as recited in claim 20, further comprisinginitializing the adapting delay based on a peak in an adaptation profileof the settle parameter.